1. Field of the Invention
The present invention relates to a disc drive apparatus and a method of manufacturing the same.
2. Description of the Related Art
In recent years, the disc drive apparatus for rotating a disc-like medium has been used, for example in a CD player or a DVD player to rotate a disc-like optical recording medium of one kind of the disc-like medium, such as a CD (compact Disc) or a DVD (Digital Versatile Disc). In the CD player or the DVD player, while the CD or the DVD is being rotated by the disc drive apparatus, recording of signals in a signal-recording layer of the CD or the DVD and/or reproduction of the signals recorded in the signal-recording layer is performed using a light beam.
Such a disc drive apparatus as described above comprises a turntable and a rotary shaft fixed concentrically to the turntable. The turntable has a boss at a center portion of its one side surface. A center hole is formed in the boss, and the rotary shaft is inserted into and fixed in the center hole. Another side surface of the turntable supports concentrically the disc-like optical recording medium, such as the CD or the DVD, which is one kind of the disc-like medium. The rotary shaft is usually an output shaft of an electric motor.
In the above-mentioned disc drive apparatus, it is necessary to rotate the disc-like medium stably and accurately at a high speed. Thus, the disc drive apparatus further comprises a damper that presses a rotation center portion of the disc-like medium, supported concentrically on another side surface of the turntable, downward to another side surface. Therefore, while the turntable is being rotated with the disc-like medium, the boss of the turntable is being subjected to a downward pressing force by the clamper and a rotation torque by the rotary shaft.
Comparing with the disc drive apparatus used in the CD player, the disc drive apparatus used in the DVD player is required to rotate the DVD more stably and accurately at a higher speed. Thus, in the disc drive apparatus in the DVD player, compared with the disc drive apparatus in the CD player, it is necessary to fix the boss of the turntable to the rotary shaft more accurately and securely.
In the conventional disc drive apparatus, the rotation center hole of the boss of the turntable is fixed to the rotary shaft only by press fitting, or by a combination of press fitting and adhesive. The fixation of the rotary center hole only by press fitting, compared with the combination of press fitting and adhesive, is weak in a strength against the above-mentioned rotation torque and pressing force, and this weak strength will be lowered further with time.
A conventional disc drive apparatus, in which a rotation center hole of a boss of a turntable is fixed to a rotary shaft by a combination of press fitting and adhesive, is well known by Japanese Patent Application KOKAI Publication No. 11-176077. In the conventional disc drive apparatus disclosed in this Publication, the turntable is pressed to fit on the rotary shaft which is one of a rotor of an electric motor, and one side surface of the turntable, which faces the rotor of the motor, is fixed by an adhesive to an end surface of the rotor, which faces to the turntable. The adhesive is applied to both of the rotor-facing side surface of the turntable and the turntable-facing end surface of the rotor, at their positions separated outward in the radial direction of the rotary shaft from the rotation centerline of the rotary shaft. In this fixation, the adhesive tends to cause a rotation unbalance of the turntable and motor rotor, and a relatively much amount of adhesive is used for the fixation.
In another conventional disc drive apparatus comprising a turntable fixed to a rotary shaft by a combination of press fitting and adhesive, the turntable has a boss at a center portion of one side surface thereof, and a center hole into which the rotary shaft is inserted and fixed is formed in the boss. Another side surface of the turntable supports concentrically a disc-like optical recording medium, which is one kind of a disc-like medium, such as a CD or a DVD. The rotary shaft is an output shaft of an electric motor.
An end portion of an inner circumferential surface of the rotation center hole of the boss, which is near to another side surface of the turntable, is chamfered conically to act as an adhesive reservoir.
In the above-mentioned another conventional disc drive apparatus, at first the rotary shaft is pressed to fit into the rotation center hole of the boss of the turntable, and then the conical adhesive reservoir is filled with an adhesive to bond the turntable to the rotary shaft.
The adhesion strength is usually weakened as a clearance to be filled with the adhesive between bonded parts (in this conventional apparatus, the conical adhesive reservoir in the inner circumferential surface of the rotation center hole of the boss of the turntable and an outer circumferential surface of the rotary shaft) is increased.
Therefore, in the above mentioned another conventional disc drive apparatus in which the adhesive is filled in the conical adhesive reservoir, the fixation or adhesion strength of the conical adhesive reservoir area of the inner circumferential surface of the rotation center hole of the boss of the turntable to the outer circumferential surface of the rotary shaft is relatively weak against the pressing force, loaded by the damper which presses the center portion of the disc-like optical recording medium supported on another side surface of the turntable, in a direction toward another side surface of the turntable along the rotation centerline of the rotary shaft.
Further, the above mentioned adhesion is also relatively weak against the rotation torque generated between the inner circumferential surface of the rotation center hole of the boss of the turntable and the outer circumferential surface of the rotary shaft by a rotation of the rotary shaft.
In still another conventional disc drive apparatus comprising a turntable fixed to a rotary shaft by a combination of press fitting and adhesive, the turntable has a boss at a center portion of one side surface thereof, and a center hole into which the rotary shaft is inserted and fixed is formed in the boss. Another side surface of the turntable supports concentrically a disc-like optical recording medium, which is one kind of a disc-like medium, such as a CD or a DVD. The rotary shaft is an output shaft of an electric motor.
The above mentioned still another disc drive apparatus is different from the aforementioned another disc drive apparatus in a following point. That is, a cylindrical large diametrical portion extending from the above-mentioned one side surface of the turntable toward another side surface is formed in an inner circumferential surface of the rotation center hole of the boss, and the cylindrical large diametrical portion terminates at a position separated from the above-mentioned one side surface of the turntable by a predetermined distance. This cylindrical large diametrical portion acts as an adhesive reservoir.
In this still another conventional disc drive apparatus, before the rotary shaft is pressed to fit into the rotation center hole of the boss of the turntable, an adhesive is applied to an area of an outer circumferential surface of the rotary shaft, that area being to be pressed to fit into the rotation center hole. And, by the above-mentioned press fitting, the adhesive is filled in the cylindrical adhesive reservoir.
In the still another conventional disc drive apparatus configured as described above, a clearance to be filled with the adhesive between the bonding parts (in this conventional apparatus, the cylindrical adhesive reservoir area of the inner circumferential surface of the rotation center hole of the boss of the turntable and the outer circumferential surface of the rotary shaft) is smaller than that of the aforementioned another conventional disc drive apparatus (in the aforementioned another conventional apparatus, the conical adhesive reservoir area of the inner circumferential surface of the rotation center hole of the boss of the turntable and the outer circumferential surface of the rotary shaft).
Therefore, in this still another conventional disc drive apparatus in which the adhesive is filled in the cylindrical adhesive reservoir, compared with the aforementioned another conventional disc drive apparatus in which the adhesive is filled in the conical adhesive reservoir, the adhesion strength of the cylindrical adhesive reservoir area of the inner circumferential surface of the rotation center hole of the boss of the turntable to the outer circumferential surface of the rotary shaft, is strong against the pressing force loaded by the aforementioned damper in the direction toward another side surface of the turntable along the rotation center line of the rotary shaft.
Further, the above mentioned adhesion in the still another conventional disc drive apparatus is also strong against the rotation torque generated by the rotation of the rotary shaft between the inner circumferential surface of the rotation center hole of the boss of the turntable and the outer circumferential surface of the rotary shaft, in comparison with the adhesion in the aforementioned another conventional disc drive apparatus.
However, in this still another conventional disc drive apparatus, when the rotary shaft is pressed into the rotation center hole of the boss of the turntable, an opening of the cylindrical adhesive reservoir in an end surface of the boss tends to be blocked by the adhesive applied to the outer circumferential surface of the rotary shaft. In this case, the air in the adhesive reservoir can not escape from the opening to an external space, and as a result, a part in the adhesive reservoir can not be filled with the adhesive. This result in that the adhesive reservoir area of the inner circumferential surface of the rotation center hole of the boss of the turntable and the outer circumferential surface of the rotary shaft can not be bonded with each other in a desired strength by the adhesive in the adhesive reservoir.